Builing a bigger bar graph

Take a gander at the Giant LED bar graph which [Chunky Hampton] recently completed (from this image we don’t think the nick name suits him). It’s simple both mechanically and electrically, but we love the look and think it would be a nice addition to your home, hackerspace, or as a children’s museum exhibit (we’re looking at you [Mr. Porter]).

The enclosure is a hunk of PVC electrical conduit. It’s got to be one of the largest sizes, but still should be found at most home stores. The base mounts easily and the cover snaps into place. [Chunky] used a hole saw to create the openings for the LED modules. They’re circular boards with multiple single-color LEDs on them. A common power bus feeds the high side of each bit, while a couple of transistor ICs controlled by 595 shift registers address them on the low side. From there just use any controller you wish, but in this case it’s an Arduino.

[Chunky] uses the meter to display power output from his stationary bicycle generator. But he also put together a little Larson Scanner demo which you can see after the break.

The first bulb just had a 1 ohm resistor in series. The other 7 bulbs each had a darlington transistor in series with it. The base of the darlington went to the supply through a zener diode and a resistor. The zeners were chosen for successively higher voltages; 11v, 12v, 13v… 17v. I actually had only 3 zener values, but added forward biased diodes in series to adjust the value in 1v increments.

The bike had a car radiator fan used as a generator. It had a skateboard wheel on its shaft that rubbed against the tire of the bike.

The power meter was an analog wattmeter that I happened to have. It probably dates back to the 1950’s.